President Obama and South Korean President Park Geun-hye during a welcoming ceremony at the presidential Blue House in Seoul on April 25. / Kim Hong-Ji, AFP/Getty Images

by Kim Hjelmgaard, USA TODAY

by Kim Hjelmgaard, USA TODAY

President Obama said Friday in Seoul that Washington stands "shoulder to shoulder" with South Korea in its rejection of a nuclearized North Korea and that it may be time to consider more sanctions against the isolated state.

Addressing a joint news conference alongside South Korean President Park Geun-hye, Obama said threats by North Korea will get it "nothing except further isolation" from the global community.

He conceded that additional sanctions may have limited impact. "We are not going to find a magic bullet that solves this problem overnight," Obama said.

"We can't waver in our intention. We have to make sure that, in strong concert with our allies, that we are continuing to press North Korea to change its approach," he said.

The president is paying a visit to South Korea as the nation continues to reel from last week's ferry disaster that left 300 people dead or missing, mostly high school students. South Korea is the second stop on a planned four-nation tour of Asia for the president.

"When our friends are in trouble, America helps, and we'll continue to do everything we can to stand with our Korean friends at this difficult time," Obama said in an interview published Friday by the South Korean newspaper JoongAng Ilbo.

In his address, Obama said he is mindful that his visit comes at "a time of great sorrow" for South Korea.

Park has been consumed by the April 16 maritime disaster. Most of the ferry's 29-member crew survived. Eleven of them, including the captain, have been arrested on suspicion of negligence or abandoning people in need as the ferry sank. Park recently likened their behavior to murder. The disaster could color the economic and security agenda she had been expected to highlight for Obama.

Meanwhile, North Korea has threatened to conduct another nuclear test, and if that happens while Obama is still in the region tensions could be further heightened.

"President Obama's visit to South Korea sends a strong message to North Korea that its provocative acts cannot be tolerated," Park said.